1. Field of the Invention
The present invention relates to a numerical controller and, in particular, to a numerical controller having a cutting in/out motion inserting function or a circular motion inserting function for an improvement in the separation of chips and the efficient circulation of a coolant.
2. Description of the Related Art
In known lathe-turning machining, a workpiece is cut in one direction with a cutting tool. Therefore, chips resulting from the machining are continuously generated without being separated as the cutting tool moves. If the machining is continuously operated with the chips remaining, the chips come in contact with the workpiece, which results in damage on the workpiece.
In addition, the cutting tool comes in contact with the workpiece at all times during the machining, and thus a coolant does not efficiently circulate between the cutting tool and the workpiece. This results in reduction in the service life of the cutting tool due to friction and reduction in machining accuracy caused when the blade tip of the cutting tool deforms due to heating.
In order to address the above problems in the related art, various methods have been proposed. For example, Japanese Patent Application Laid-open No. 2013-103279 describes a machine tool in which a numerical controller vibrates a workpiece as a machining target, a cutting tool for machining, or both the workpiece and the cutting tool with low frequency in at least a biaxial direction to achieve the separation of chips and the circulation of a coolant. Further, Japanese Patent Application Laid-open No. H06-285701 describes a machine tool in which a numerical controller executes the forward movement, the suspension, and the reverse movement of lathe-turning machining at any timing to prevent the continuous generation of chips. Furthermore, each of Japanese Patent Application Laid-open Nos. 2006-001008, 2002-292501, H07-068401, H01-092001, and 2009-190119 propose a machine tool in which vibration is applied to a cutting tool by an actuator mechanism (piezoelectric element or the like) attached to a cutting tool holder or the like to cause the same to execute circular motion or elliptic motion.
However, such related arts suffer from the following problems.
In the machine tool described in Japanese Patent Application Laid-open No. 2013-103279, it is required to apply low-frequency vibration to a workpiece and a cutting tool. With a configuration that applies low-frequency vibration, however, ball screws used in a feeding mechanism causes a backlash. In order to reduce the impact of the backlash, it is required to increase the amplitude of the low-frequency vibration and the feeding speed of the feeding mechanism. In this regard, it may also be possible to use a linear motor that is free from the backlash. However, the linear motor results in an increase in the size, the weight, and the cost of the whole machine tool compared with the ball screws.
In addition, in the machine tool described in Japanese Patent Application Laid-open No. H06-285701, the numerical controller executes the forward movement, the suspension, and the reverse movement of the lathe-turning machining with the blade tip of the cutting tool coming in contact with the workpiece. Therefore, there is a likelihood that the cutting tool comes in contact with a processed machining surface to be damaged.
Moreover, in each of the machine tools described in Japanese Patent Application Laid-open Nos. 2006-001008, 2002-292501, H07-068401, H01-092001, and 2009-190119, it is required to attach the actuator mechanism to the cutting tool holder or the like, which results in an increase in the cost of the machine tool.